The recapping of tires has heretofore been accomplished by first building up a layer of uncured rubber on a buffed tire carcass. Sometimes a flexible ring mold having a negative tread pattern imprint is then placed around the built-up tire and the whole assembly placed in a sealing envelope. This whole assembly is then placed into a vulcanizing chamber and the rubber is cured with the imprint of the mold contained therein.
During placement of the mold over the built-up tire, the mold must be stretched and expanded to allow the tread pattern to fit around the built up tire. Alternatively, the tire must be "buckled" to receive the mold and then inflated against the mold. During curing of the rubber with the mold so disposed, the rubber assumes a plastic state, thereby allowing the mold tread pattern to sink into the rubber to form the positive contour of the tread. This process is normally assisted by some form of external force such as high chamber pressure applied to the mold, the aspiration and resiliency of the sealing envelope or pressure applied to the build up tire to force outward against the mold.
More recently, pre-cured tread material has been utilized for recapping. Such pre-cured tread material has the tread formed therein, eliminating the need for a tire tread mold. In using the "pre-cure", a bonding gum is inserted between the retread material and a tire carcass and heat is applied to cause the "pre-cure" to adhere to the carcass.
The aforementioned process required the use of vent string, vent straps and perforated members to permit air flow into and out of the curing envelope.
The use of materials such as the vent strings, vent straps and the use of polypropylene films that are perforated to permit air to flow between the curing envelope and the mold frequently require such items to be stapled to the tire. Sometimes the stapling results in small pinhole leaks. In any event, the use of such materials requires additional time to apply those materials during the retreading process. The additional time and materials increase the cost of the retreading or recapping.